Long-term effects of vegetation control treatments for release of Engelmann spruce from a mixed-shrub community in Southern British Columbia

Abstract

-In British Columbia, vegetation management treatments are widely used to ensure successful establishment of young stands and achievement of free-growing requirements. A study was established in 1991 to examine the effectiveness of vegetation control treatments for release of Engelmann spruce (Picea engelmannii Parry) seedlings from a mixed-shrub community. The study consisted of eight treatments replicated three times in a completely randomized design. The treatments comprised six combinations of spring, summer and annual repeated manual cutting, a single application of glyphosate, and an untreated control. Controlling the mixed-shrub community one-year after planting using glyphosate and manual cutting treatments significantly improved spruce survival. Repeated manual cutting significantly improved survival over that achieved with only a single treatment. Consequently, the density of well-spaced trees was significantly increased in the repeated manual cutting and glyphosate treatments. In 2001, the untreated control only has 27% of well-spaced spruce trees that are free growing compared to more than 50%, 75% and 83% in single cutting, repeated manual cutting and glyphosate treatment, respectively. Treatments significantly increased height and groundline diameter from the third through the seventh year but not in year ten. Continued mortality of suppressed seedlings after year seven is a probable cause of lack of treatment differences in the tenth year. However, height-to-diameter ratio was significantly reduced in year ten for all treatments over the control and for repeated versus single cutting treatments. Ten-years after treatment, significant differences in vegetation community percent cover, richness, and diversity were not detected among treatments.Engelmann spruce / vegetation management / repeated manual cutting / glyphosate / free growing Résumé -Effets à long terme de traitements de contrôle de la végétation effectués pour dégager des épicéas d'Engelmann concurrencés par divers arbustes, en Colombie Britannique méridionale. En Colombie Britannique, on fait largement appel à des traitements de gestion de la végétation pour faciliter l'installation des jeunes peuplements et leur permettre de se développer librement. Une étude a été engagée en 1991 pour juger l'efficacité de traitements de contrôle de la végétation visant à dégager des épicéas d'Engelmann (Picea engelmanii Parry) concurrencés par divers arbustes. Cette étude comportait huit traitements, répétés trois fois selon un dispositif en blocs complets. Pour les traitements, il s'agissait de six combinaisons de dégagements par coupe effectués au printemps ou en été pendant une ou plusieurs années, d'une seule application de glyphosate, et enfin d'un témoin sans intervention. Le contrôle de la végétation arbustive par application de glyphosate un an après plantation, ou par les traitements dégagement par coupe, se traduit par une amélioration significative de la survie des épicéas. Des dégagements répétés pendant plusieurs années se révèl...

Effects of competing vegetation on juvenile white spruce (Picea glauca (Moench) Voss) growth in Alaska

“…Future measurements will be needed to confirm this observation. Results from other spruce vegetation management studies [3,30] have also indicated that longerterm observations may differ from early results, emphasizing the importance of longer-term studies when evaluating vegetation management treatments.…”

Modelling vegetation management treatments with the Tree and Stand Simulator

“…If left untreated this mixed-shrub complex can reduce survival and growth of planted spruce through reduction in light levels and induced vegetation and snow press. Significant improvement in spruce survival was noted for the repeated manual brushing and glyphosate treatments; however, significant height growth differences were limited to years 4 to 5 and diameter growth to years 3 to 7 post-treatment (Biring et al 2003).…”

“…The 10-year post-treatment results from these two trials have been previously published (Biring et al 2003, Harper et al 2005 and represent some of the oldest stand-level, vegetation management datasets presently available from British Columbia. The objectives of this paper are to explore the long-term growth and yield predictions for the various vegetation management treatments and to compare the TASS results in terms of merchantable volume, physical rotation age and stand productivity.…”

“…Vegetation and crop tree response data have been published for both these research sites (Harper et al 1998, Comeau et al 2000, Biring et al 2003, Harper et al 2005. For more detailed information please refer to these publications.…”

“…Mean site index was determined from treatment top height and breast height age (BHA) using the site curves of Thrower and Goudie (1992) for Douglas-fir and, Chen and Klinka (2000) for Engelmann spruce (Table 1). The results of previous height growth analysis (Biring et al 2003, Harper et al 2005 were used to determine if unique treatment site indices were justified assuming any increase in the rate of early stand height development followed a type I response associated with weed control (Snowdon and Waring 1984).…”